Conventionally, there has been known a torsion damper including a disc-shaped inertia body connected to a crankshaft of an engine and rotating around an axis of the crankshaft, and a damper spring interposed between the crankshaft and the inertia body (for example, see Patent Documents 1, 2). Such a torsion damper shows dynamic damping effect by vibrating in opposite phase with respect to torsional vibration to be input (hereinafter, also simply referred to as input vibration) at a resonance frequency (natural frequency) f0 indicated by the following equation.f0=½π√(k/m)
where k is a spring constant of a damper spring, and m is a mass of the inertia body